Specimen paper: Police attended a collision caused by ice on the road at 10.20.
The gritter had been along the road three and a half hours previously. At what time
( in 12 hour time ) had the road been gritted?

Note: 10.20 is confusing. You need to assume, since this is unclear, that you are
in 24 hour time. (24 hour time should read 1020 without the dot).

This question is in two parts:
a) Count back in time (again, remember 60 minutes in the hour)
10.20 - 3½ hours = 6.50
b) Convert from the 24 hour clock to the 12 hour clock (am or pm)
(equivalent time in 24 hour clock = 0650)
Answer = 6.50 am

Police Practice Papers, Number test 7, Question 16: A chartered flight took off at 0935
hours. It arrived at its destination at 1820 hours.
a) At what time (in 12 hour time) did the plane take off?
b) At what time (in 12 hour time) did the plane arrive?
c) How long did the flight take?

For a) and b) you are required to convert 24 hour time to 12 hour time: am is used for the 12 morning hours up to noon (or midday)
pm is used for the remaining 12 hours from noon to midnight
a) 0935 hours = 9.35 am
b) 1820 hours = 6.20 pm
c) 0935 to 1820 = 25 mins + 8 hours 20 mins = 8 hours 45 mins
Answer = 8 hours 45 mins

Don’t get hung up on technicalities: you are not asked to calculate noon or midnight times,
only from one clock to another. The following table might help:

12 hour clock am/pm 24 hour clock
12.00 am 0000 hours
1.00 am 0100 hours
8.30 am 0830 hours
12 pm 1200 hours
5.15 pm 1715 hours
9.20 pm 2120 hours
11:59 pm 2359 hours
12 am 0000 hours

Remember for 12 hour time, you need to include am or pm in the answer to get the mark.
For 24 hour time, you need four digits, no dot in the middle and hours at the end.